Chelates are generally produced by the reaction or association of a ligand with a metal cation, resulting in a complex. Amino acid chelates may be made by the reaction of an α-amino acid and metal ion typically, but not necessarily, having a valence of two or more to form a ring structure. In such a reaction, the positive electrical charge of the metal ion is neutralized or delocalized by the electrons available through the carboxylate and or free amino groups of the α-amino acid. The structure, chemistry and bioavailability of amino acid chelates is well documented in the literature, e.g. Ashmead et al., Chelated Mineral Nutrition, (1982), Chas. C. Thomas Publishers, Springfield, Ill.; Ashmead et al., Intestinal Absorption of Metal Ions, (1985), Chas. C. Thomas Publishers, Springfield, Ill.; Ashmead et al., Foliar Feeding of Plants with Amino Acid Chelates, (1986), Noyes Publications, Park Ridge, N.J.
One advantage of using amino acid chelates in the field of mineral nutrition is that they are readily absorbed in the gut and mucosal cells by means of active transport. Chelates enable minerals to be absorbed in biological processes along with amino acids as a single unit utilizing the amino acids as carrier molecules. Therefore, the problems associated with the competition of ions for active sites and the suppression of specific nutritive mineral elements by others can be avoided. Controlled delivery of nutritional minerals is advantageous because large quantities of those minerals often cause nausea and other discomforts as well as create an undesirable taste.
Since metal amino acid chelates serve as a delivery means for mineral supplements in the fields of plant nutrition, animal feed, and human nutritional supplements, there is a growing need for methods of characterizing chelates, and particularly quantitative assessment of bound and unbound metal amounts in formulations. The use of spectroscopic means, such as Fourier Transform infrared spectroscopy (FTIR), to characterize chelates is limited. Such techniques are sensitive to water present in the sample, and therefore, make it difficult or impossible to determine the amount of unbound metal in solution for a metal chelate. A technique that can quantify the amount of unbound metal, in chelate formulations, particularly in solution, is highly desirable since that technique could be used in the agricultural and nutritional supplement industries to attain reliable measures for comparisons and standards of formulary products and ingredients.